The "iron law of prohibition" explains why the DEA is responsible for the fentanyl crisis

As a result of the prohibition of alcohol in the United States, the supply of beer and wine decreased while that of hard liquor increased. Bootleggers realized they could make more money and be less likely to be caught smuggling one crate of whiskey instead of 20 cases of beer. Alcohol prohibition led to the creation of organized crime syndicates that trafficked in drugs and other illegal goods such as alcohol, prostitutes, and gambling, and much of that ill-gotten money flowed into the pockets of government officials who supported prohibition.

The United States' racist war on drugs is another example of prohibition leading to a worse outcome. After decades of trying to block the flow of heroin into the United States, the Drug Enforcement Administration has created a huge market for fentanyl, which is at least 50 times stronger than heroin.

From Vice:

Sanho Tree, a drug policy expert for the Institute for Policy Studies, called the transition from heroin to fentanyl "a logical evolution of this market."

Tree brought up a well-known drug analysis from the 1980s known as "the iron law of prohibition" that has proved to be prescient in predicting the current fentanyl epidemic.

"As you crack down on the original substances, you end up with a substitute that is usually more compact, more potent, easier to smuggle and more problematic, more dangerous," Tree told VICE World News.

Prohibition is a response to the failure of prohibition.